Half Vertical
W4ULD
In his Aerials column in the August 2009 issue of World Radio On Line, Kurt Sterba described an antenna constructed by a reader and called it a Half Vertical. The antenna is essentially an ungrounded L antenna or a 40 M dipole with one leg horizontal and one leg vertical. The reader had been using a 135 ft. all-band antenna which I presume was a centerfed Zepp. This antenna blew down and was replaced with the Half Vertical. cut for 40M. The reader did not describe the orientatioin of either antenna or the feed line he was using but claimed a phenomenal improvement is signal strength (I presume on 40M) with the Half Vertical.
I modeled the Half Vertical with EZNEC +4 and compared it to a 135 ft. dipole. Since no feedline data were provided, I had to compare the gains of both antennas without feedline losses. Since the Half Vertical was bent at the feedpoint I used the split source option. The EZNEC file of the Half Vertical is halfvertical40.EZ. The file for the 135 ft Zepp on 40M is 135dipole7.22.EZ.
The azimuth plots of the two antennas are attached. The Half Vertical had a maximum gain of 2.6 dBi approximately broadside of the horizontal element. Off the end of the horizontal element the gain was about -1.9 dBi. Off the feedpoint end the gain was less than 2 dB down from the maximum. The Zepp showed broadside gain at an elevation angle above 45 degrees so I made the plot at 45 degrees elevation. The broadside gain was 7.28 dBi and about 15 dB down off the ends. Since antenna orientation was not specified, these data cannot be interpreted. However, assuming the same orientation of the horizontal elements, the 135 ft. dipole should have a maximum signal strength almost one S unit better than the Half Vertical.. On the other hand, if the reader was comparing the strength of stations off the end of the dipole or in null, signals for the Half Vertical would have been much better. This again illustrates the advantage of a vertical antenna. Assuming that one uses at least 30 radials to reduce ground loss, a vertical will outperform a 135 ft. all-band Zepp, especially in the nulls of the Zepp at the higher frequencies.
If we assume 100 ft. CQ-552 ladder line feeding the Zepp,..2 dB loss for the balun,
and .01 dB for the tuner, The maximum gain of the Zepp at 45 degrees elevation would be 5.9 dBi. If we assume .2 dB loss for the balun
used with the half vertical and .55 dB loss for 100
ft. RG-213 coax, the maximum gain of the half vertical is reduced to 1.77 dBi. So it is clear
that antenna orientation and/or direction of the stations worked had to be the
important factors for a significant improvement in signal strength with the
half vertical.
